Here's a place where I can post my thoughts on new papers, provide updates on my projects, and post info that will eventually be on my website The Theropod Database - http://theropoddatabase.com/ . It will center on theropods, but may delve into other topics as well such as phylogenetics.

Tuesday, November 23, 2010

January 1, 201n is fast approaching along with what will no doubt be a rush to define clades. The major clades' definitions are already written up for Phylonyms, but there's still hope we can salvage ideal definitions for smaller groups. It's my hope that authors will use this as a reference to see why certain definitions should and shouldn't be used before they try to register them.

First, some basic rules.
1. If the clade is named after a genus, use the type species of that genus as an internal specifier. It doesn't matter if it's indeterminate, poorly known or not well nested because it has to belong to the clade in question or else the clade would need a different name. For example, Sereno defined Alvarezsauridae using Shuvuuia, but if the more poorly known and more basal Alvarezsaurus didn't belong, we couldn't keep calling Shuvuuia's clade Alvarezsauridae anyway.
2. If the clade isn't named after a genus, use the type species of one of the genera originally included by the clade's author as an internal specifier.
3. Whenever possible, use external specifiers that were thought by the clade's author to not belong to it.
4. Strive to make the definition congruent with all suggested topologies, not just your own. It's naive to think we have the right phylogeny today.
5. If a more than one definition follows the above rules, use the one proposed first.

Avepoda Paul, 2002Definition- (metatarsal I does not contact distal tarsals homologous with Passer domesticus) (modified from Paul, 2002)Comments- Paul used "Neotheropoda", so Passer domesticus is used since of the two internal neotheropod specifiers, only it has a preserved first metatarsal.

Averostra Paul, 2002Definition- (promaxillary fenestra homologous with Dromaeosaurus albertensis) (modified from Paul, 2002)Comments- Paul's definition used the less specific Dromaeosauridae and did not indicate which accessory maxillary opening should be used. The promaxillary fenestra is specified, since basal averostrans of Paul only have it, and not a maxillary fenestra. Ezcurra and Cuny's (2007) node-based definition is not used because it postdates Paul's for a taxon Paul created, and is a junior synonym of Neotheropoda.

Coelophysoidea Nopcsa, 1928 sensu Holtz, 1994Definition- (Coelophysis bauri <- Ceratosaurus nasicornis, Passer domesticus) (first order revision of Padian et al., 1999)Comments- Sereno's (1998) definition used Carnotaurus, but abelisaurids have been sometimes seen as carnosaurs (Kurzanov, 1989) and Ceratosaurus has been consistantly used in phylogenies due to its early discovery. Sereno (online) suggested adding Passer, which is good for phylogenies like Raath's (1984) and early ones where birds derived from Coelurosauria sensu Huene (e.g. Barsbold, 1984). Is it too much to ask for Podokesauroidea being (Podokesaurus holyokensis <- Ceratosaurus nasicornis, Passer domesticus)?

Dilophosauridae Madsen and Welles, 2000Definition- (Dilophosaurus wetherilli <- Coelophysis bauri, Allosaurus fragilis) (new)Comments- This hasn't been defined yet, but besides the obvious Coelophysis, I think Allosaurus is better than Passer since it covers older topologies where Dilophosaurus was carnosaurian AND newer ones where we just need a tetanurine specifier.

Procompsognathidae/inae- Given a definition by Sereno (1998), this seems unwise until more than his studies indicate a need for such a clade, and until Procompsognathus' position even as a theropod is more established.

Coelophysidae Nopcsa, 1928 sensu Welles, 1984 Definition- (Coelophysis bauri + Megapnosaurus rhodesiensis + "Megapnosaurus" kayentakatae) (Holtz, 1994)Comments- Though Paul (1988) and Novas (1991, 1992) included Dilophosaurus, Welles did not and Coelophysoidea is well established as that larger clade. Sereno (1998) used Procompsognathus as an internal specifier, but it's been placed outside Coelophysoidea by some authors (Gauthier, 1984; Paul, 1984, 1988; Allen, 2004) so this is not recommended. Tykoski and Rowe (2004) left out kayentakatae, but Holtz's including it lets us use Coelophysinae for that smaller clade.
Incidentally, if we were allowed to start over, I would use Podokesauridae and define it as (Podokesaurus holyokensis <- Liliensternus liliensterni, Coelurus fragilis, Compsognathus longipes) for this family. This covers Coelophysis as well, since Podokesaurus shares longer dorsal centra with it than Liliensternus shows.

Segisaurinae Camp, 1936 sensu Kalandadze and Rautian, 1991Definition- (Segisaurus halli <- Coelophysis bauri) (new)Comments- Since Segisaurus is always outside (Coelophysis+Megapnosaurus) in phylogenies, this gives some structure to coelophysid relationships and is equivalent to Sereno's Procompsognathinae but uses a more stable genus.

Coelophysinae Nopcsa, 1928Definition- (Coelophysis bauri <- Segisaurus halli) (new)Comments- Sereno (1998) used Procompsognathus as the internal specifier as he had it in a clade with Segisaurus outside Coelophysinae. Thus this definition retains his concept. None of the taxa used by Nopcsa as non-coelophysine podokesaurids are useful today (Podokesaurus, Procerosaurus, Saltopus, Tanystropheus), and he only included Coelophysis in the subfamily.

Neotheropoda Bakker, 1986Definition- (Ceratosaurus nasicornis + Passer domesticus) (modified from Padian et al., 1999)Comments- Sereno (1998) used Coelophysis as an internal specifier, but podokesaurids were specifically excluded by Bakker. I considered also using Allosaurus, but Ceratosaurus has never been closer to birds than Allosaurus in any topology with coelophysoids outside a Ceratosaurus+Allosaurus clade, and all the authors to use Neotheropoda have theropod birds. Although the clade now fails under a BAND phylogeny, using Allosaurus instead of Passer would make it fail under the more likely phylogeny where Ceratosaurus is a carnosaur.

Ceratosauria Marsh, 1884Definition- (Ceratosaurus nasicornis <- Allosaurus fragilis, Passer domesticus) (first order revision of Rowe, 1989)Comments- Rowe and Gauthier's (1990) definition was node-based and used every ceratosaur they recognized, which is less stable especially since most are coelophysoids. Sereno's (1998) used Coelophysis, which doesn't work in many phylogenies since it's outside Ceratosaurus+tetanurines. I think Allosaurus would be a good taxon to add, to account for the many early phylogenies where Ceratosaurus was a carnosaur (e.g. Bonaparte et al., 1990, Currie, 1995) and those where birds aren't dinosaurs. It also makes sense as a distinctly non-ceratosaurian theropod of both Marsh and Gauthier.

Neoceratosauria Novas, 1991Definition- (Ceratosaurus nasicornis + Abelisaurus comahuensis) (modified from Holtz, 1994)Comments- Padian et al. (1999) used a stem away from Coelophysis, but in most modern topologies that would include tetanurines as well. There's controversy over using this compared to Ceratosauroidea Bonaparte et al., 1990. Neoceratosauria is used far more often, was named unofficially before Ceratosauroidea (in Novas' 1989 thesis) and has been given a more useful definition (Ceratosauroidea's is Ceratosaurus<-Coelophysis).

Abelisauria Novas, 1992Definition- (Abelisaurus comahuensis + Noasaurus leali) (modified from Novas, 1997)Comments- Both Abelisauroidea and Abelisauria were created for the same purpose- to separate abelisaurids and noasaurids from ceratosaurids. I suppose ideally, I'd switch their definitions since -ia suggests a more inclusive clade than -oidea.

Abelisauridae Bonaparte and Novas, 1985Definition- (Abelisaurus comahuensis <- Noasaurus leali, Ceratosaurus nasicornis, Elaphrosaurus bambergi, Allosaurus fragilis) (new)Comments- Most definitions have used Carnotaurus as the internal specifier, which is wrong since it isn't the eponymous genus. The other two are node-based using taxa with uncertain placements, while the above definition is stable and covers all proposed topologies.

Carnotaurini- I would leave this undefined, since Coria et al.'s original definition could easily be more inclusive than Carnotaurinae, and having Carnotaurus and Aucasaurus as sister taxa isn't supported by recent analyses.

Comments- Megalancosaurus preonensis was discovered in 1980 and originally assigned to Pseudosuchia sensu Huene (Calzavara et al., 1980). Although Carroll (1988) also placed it in Thecodontia (in the traditional paraphyletic sense), generally only those workers who reject cladistics and a dinosaurian origin for birds have continued to call Megalancosaurus an archosaur (e.g. Feduccia and Wild, 1993; Feduccia, 1996). This is almost exclusively based on its supposed antorbital fenestra (considered near certainly absent by Renesto and Dalla Vecchia, 2005), and presumably the need to have birds derive from archosaurs. Megalancosaurus is currently placed in the larger clade Simiosauria, which has a highly uncertain placement among eosuchians. Various analyses place them outside Neodiapsida, sister to Euryapsida, in Lepidosauromorpha, as non-thecodont archosauromorphs or as 'protorosaurs', with the latter three possibilities sometimes including a close relationship with pterosaurs. Determining their relationships will require a larger diapsid phylogenetic analysis than those currently published.

Megalancosaurus a theropod? Olshevsky (1991) believed Megalancosaurus to be a basal theropod (or in his taxonomy, a basitheropod theropodomorph), but this was based only on the holotype. Of the theropodomorph characters he lists, carnivorous dentition is primitive for gnathostomes, while new specimens show Megalancosaurus lacks erect limbs and a reduced calcaneum. Of Olshevsky's basitheropod characters, an antorbital fenestra is primitive for archosauriforms and probably lacking in Megalancosaurus, "generally avian appearence of the skull" is vague and unlike basal theropods, relatively large forelimbs are primitive for tetrapods and unlike basal theropods, "clavicles, fused clavicles, or primitive furcula" covers every possibility and Megalancosaurus' are unfused which is primitive for tetrapods, and pentadactyl manus and pes are plesiomorphic for tetrapods and not found in basal theropods. The tarsus is not even incipiently mesotarsal and as noted above the calcaneum is not reduced. Megalancosaurus does share the presence of at least three sacral vertebrae with dinosaurs, but this is present in pterosaurs and some other taxa as well. Furthermore, the more basal Vallesaurus and Drepanosaurus only have two sacrals. While Megalancosaurus and theropods both have manus capable of grasping, in theropods digit I is angled towards II and III due to an asymmetrical metacarpal I articulation and twisted phalanx I-1, whereas in Megalancosaurus half the digits oppose the other half due merely to a lack of articulation between the metacarpals. This suggests the grasping abilities are convergent.

Megalancosaurus a bird ancestor? Feduccia and Wild (1993) first suggested Megalancosaurus was more closely related to birds than theropods were, though the absence of other taxa in their cladogram leaves one uncertain exactly where in Archosauria they place the the Megalancosaurus+bird clade. The expanded braincase is also present in pterosaurs and coelurosaurs. Large orbits are found in those two groups as well, and many other small tetrapods. A pointed snout is also present in many maniraptoriforms, pterosaurs, most 'protorosaurs', choristoderes, thalattosaurs, and some basal lepidosauromorphs. The "large, oval preorbital fenestra" is actually the external naris. The reduced premaxillary dentition is not present in basal birds, though the authors state it "may be important, because when modern birds loose their teeth they loose the maxilla that houses them, and in the Cretaceous toothed birds, the teeth are borne only on the maxilla." Even ignoring the fact Aves does retain a maxilla, and subsequently discovered birds like omnivoropterygids and longipterygids have toothed premaxillae and toothless maxillae, mere propensity for a group to exhibit a character is not a synapomorphy. The dentary is said to be birdlike, but this is too vague to evaluate. The foramen magnum is claimed to be posteroventrally oriented, but this is based solely on the angle of the quadrate and ventral squamosal process. The latter is also true in Icarosaurus, the basal squamate Tamaulipasaurus, the basal choristodere Lazarussuchus, Cosesaurus and pterosaurs. Feduccia and Wild state "the six to seven elongate cervical vertebrae create a highly movable birdlike neck." The high mobility is caused by heterocoelous centra, which are similar to ornithuromorphs but not basal birds. Elongate cervical centra are present in coelurosaurs, 'protorosaurs' and other taxa, while birds have at least nine cervicals. Though the authors claim the "anterior limbs, without manus, are proportionately similar to those of modern birds and Archaeopteryx; and dissimilar to theropods," the radiohumeral ratio of 68% is shorter than most maniraptorans (even taxa known in 1993, e.g. Oviraptor 87%, Deinonychus 76%) and Archaeopteryx (84-96%), while modern birds usually have ratios of more than 100%. The large manual ungual flexor tubercles are said to be birdlike, but these are absent in the more basal Hypuronector, and also found in most theropods and pterosaurs. Contra Feduccia and Wild, the forelimbs minus manus are not longer than the hindlimbs minus pes, being 72% as long instead. Finally, the straplike scapula is indeed superficially like Aves in being extrenmely slender, bowed and having a tapered distal end. Yet basal birds lack these features, and only have scapulae as slender as pterosaurs and most theropods.

Feduccia later (1996) refers to Megalancosaurus' "tiny isodont teeth set in sockets", but they are actually subthecodont as in most basal diapsids, while isodonty is also plesiomorphic.

After the mid-1990s, Feduccia and other Birds Are Not Dinosaurs supporters seem to have reduced their emphasis on Megalancosaurus' relationship with birds. Geist and Feduccia (2000) repeat the 1993 observations, but then state "though probably not the avian ancestor, Megalancosaurus represents a chronologically and biophysically plausible model for a gliding stage through which birds must have passed." Martin (2004) incorrectly stated Megalancosaurus has a furcula, but did not explicitly link it to bird origins.

Besides those characters noted above that exclude Megalancosaurus from Theropoda, it is less similar to basal birds than even basal coelurosaurs are in many other ways. These include the absence of pleurocoels, less than five sacral vertebrae, absence of a transition point in the tail, unfused clavicles, small distal carpal I, metacarpal III longer than II, presence of manual digits IV and V, absent pubic boot, absent obturator process, obturator foramen in pubis, astragalus without tall ascending process, robust metatarsus, metatarsal I reaching tarsus, and phalanx V-1 present.

Renesto, 2000. Bird-like head on a chameleon body: New specimens of the enigmatic diapsid reptile Megalancosaurus from the Late Triassic of northern Italy. Rivista Italiana di Paleontologia e Stratigrafia. 106(2), 157-180.

Renesto, Spielmann, Lucas and Spagnoli, 2010. The taxonomy and paleobiology of the Late Triassic (Carnian-Norian: Adamanian-Apachean) drepanosaurs (Diapsida: Archosauromorpha: Drepanosauromorpha). New Mexico Museum of Natural History and Science Bulletin. 46, 1-81.

Friday, November 19, 2010

To celebrate the new look of the Theropod Database Blog, here's the new entry for Theropoda for the upcoming update of the Database. It excludes the section discussing Gonipoda, Harpagosauria and Carnosauriformes, which was featured in a prior post. Unfortunately, my favored phylogenetic definition won't be the one set by the Phylocode, though theirs is better than the other three listed here at least.

Diagnosis- [upcoming]Other diagnoses- Marsh's (1881) original diagnosis consisted largely of plesiomorphies- carnivorous; limb bones hollow; digits with prehensile claws; digitigrade pes. The distal pubes are only fused in adult neotheropods. "Vertebrae more or less cavernous" refers to the extremely constricted dorsal centra of Allosaurus, which aren't present in most theropods. "Post-pubis present" probably refers to Allosaurus' elongate pubic boot, which is only present in some avetheropods.
Marsh (1884) added more plesiomorphies- premaxilla toothed; external nares placed anteriorly; large antorbital fossa; forelimbs short; propubic pelvis.
[more will be listed of course, though this will be a long process since so many authors have diagnosed Theropoda]

Comments- Marsh (1881) named Theropoda as a dinosaur suborder containing only the Allosauridae, in which he placed Allosaurus, Creosaurus and Labrosaurus (both of the latter now recognized as synonyms of Allosaurus). By 1884, Marsh had raised Theropoda to an order and expanded it to include all carnivorous dinosaurs, as well as what are today recognized as basal sauropodomorphs (often mixed with cranial elements of canivorous crurotarsans). This was the standard for many decades, as seen in Romer's (1956) classic work, in which theropods consist of coelurosaurs, carnosaurs and prosauropods. The monophyly of theropods was questioned by Huene (1914), who placed most of the larger taxa such as Allosaurus and Megalosaurus in Sauropodomorpha (his Pachypodosauria) while the smaller taxa (which he named Coelurosauria) had branched off earlier. In the 1960's, workers began to recognize the monophyly of coelurosaurs and carnosaurs to the exclusion of basal sauropodomorphs (e.g. Colbert, 1964). Paul (1984) was the first author to use a theropod phylogeny similar to todays, with deinonychosaurs (albeit paraphyletic), tyrannosaurids, allosaurids, Eustreptospondylus, Ceratosaurus and coelophysoids forming successively more distant sister taxa to birds. Gauthier's (1984) thesis also had a modern topology, with deinonychosaurs, ornithomimids, carnosaurs and ceratosaurs (the latter two improbably inclusive, containing tyrannosaurids and coelophysoids respectively) successively further from birds, and is the basis of our current nomenclature for major clades.

Theropoda defined- Gauthier (1986) was the first to phylogenetically define Theropoda, as "birds and all saurischians that are closer to birds than they are to sauropodomorphs." Variations on this definition have been most common, with Sereno (1998) using Neornithes and Saltasaurus, specified by Sereno (2004) as Passer domesticus and Saltasaurus loricatus. Holtz and Osmolska (2004) chose Cetiosaurus oxoniensis as the sauropodomorph specifier instead. However, this class of definition violates Phylocode Recommendation 11A- "Definitions of converted clade names should be stated in a way that attempts to capture the spirit of traditional use to the degree that it is consistent with the contemporary concept of monophyly." While birds are currently thought to be theropods, this was not the consensus until over a century after Theropoda was named. Similarly, Clarke et al.'s (2004) definition using Plateosaurus engelhardti as an external specifier is problematic since basal sauropodomorphs were often included in Theropoda until the 1960s. Kischlat (2000) suggested all taxa closer to Allosaurus than to Morosaurus, which is valid in using taxa Marsh (1881) and everyone since have recognized as being theropod and non-theropod. This definition is modified here by including the types species of each genus.

Ex-theropods- Numerous taxa (at least 130) have been incorrectly placed in Theropoda in the past, including ornithosuchids, poposaurids, most basal avemetatarsalians and basal sauropodomorphs, and many Triassic archosauriforms known only from teeth. This site will have an entire section devoted to ex-theropods, so they are not discussed further here.

References- Cope, 1866. [On the anomalous relations existing between the tibia and fibula in certain of the Dinosauria]. Proceedings of the Academy of Natural Sciences of Philadelphia. 18, 316-317.

Marsh, 1881. Principal characters of American Jurassic dinosaurs. Part V. American Journal of Science. 21, 417-423.

Marsh, 1884. Principal characters of American Jurassic dinosaurs. Part VIII. The order Theropoda. American Journal of Science. 27, 329-340.

Kischlat, 2000. Tecodoncios: A aurora dos Arcosaurios no Triassico. in Holz and De Rose (eds.). Paleontologia do Rio Grande do Sul. 273-316.

Clarke, Gauthier, de Queiroz, Joyce, Parham and Rowe, 2004. A phylogenetic nomenclature for the major clades of Amniota Haeckel 1866, with emphasis on Aves Linnaeus 1758. First International Phylogenetic Nomenclature Meeting, Abstracts. 30.

Thursday, November 18, 2010

Finally customized the design to have wider posts, so that my paragraphs appear more manageable. Also changed the color scheme and added a better background with my drawings. First person to guess all the illustrated taxa wins... er... five Theropod Database Points.

Wednesday, November 17, 2010

There are two undescribed potential basal theropods from the Ischigualasto Formation, both currently described largely in abstracts.

undescribed possible theropod (Sereno, 2007)Norian, Late Triassic
Valle de la Luna Member of the Ischigualasto Formation, San Juan, Argentina
Material- (~1.6 m) incomplete skeleton including maxilla, cervical vertebrae, distal caudal vertebrae, carpus, manus, pubis, femur and tibia
partial skeletonsComments- This taxon has only been described in an abstract by Martinez et al. (2008) so far, though the official description is under review. Sereno (2007) states this is a closely related taxon to Eoraptor lunensis, while Martinez et al. (2008) place it as a basal theropod presumably closer to avepods than Eoraptor and herrerasaurids based on several mentioned characters. Phylogenetically informative characters include- promaxillary fenestra; cervical pleurocoels; distal caudal prezygapophyses ~15% of centrum length; pentadactyl manus; extensor pits on metacarpals; pubis distally tapered; pubis posteriorly curved; anterior fossa above distal condyles on femur; tibia longer than femur. Noted additional differences from Eoraptor include more gracile elements, and slender anterior maxillary teeth which are more than twice as long as the former genus.References- Sereno, 2007. The phylogenetic relationships of early dinosaurs: A comparative report. Historical Biology. 19(1), 145-155.
Martinez, Sereno and Alcober, 2008. A new basal theropod from the Ischigualasto Formation of San Juan Province, Argentina. in Calvo, Valieri, Porfiri and dos Santos (eds.). Libro de Resumenes, III Congreso Latinoamericano de Paleontologia de Vertebrados. Universidad Nacional del Comahue, Neuquen, Argentina. 153.

undescribed herrerasaurid (Ezcurra and Novas, 2007)Late Carnian-Early Norian, Late Triassic
Cancha de Bochas Member of the Ischigualasto Formation, San Juan, Argentina
Material- (MACN-PV 18.649a) (small) vertebrae, distal ulna, carpus, manus, pedal phalangesDiagnosis- (after Ezcurra and Novas, 2007) manual unguals with a posteriorly bifurcated lateral groove.
(after Ezcurra, 2010) manual phalanx II-1 with conspicuous longitudinal ridge on its proximolateral border.Comments- This specimen was discovered in the 1960s, but not noted until an abstract by Ezcurra and Novas (2007). That paper and Ezcurra (2010) placed it in Herrerasauridae, the latter using a version of Yates' sauropodomorph analysis. It was a herrerasaur based on- manual phalanx I-1 longer than metacarpal I; strongly curved manual unguals; metacarpals IV-V ventral to the others. While these are shared with Herrerasaurus, the unknown forelimb of Staurikosaurus makes the relationship between these three taxa uncertain. The new taxon will be described in more detail by Ezcurra and Novas (in prep.).References- Ezcurra and Novas, 2007. New dinosaur remains (Saurischia: Herrerasauridae) from the Ischigualasto Formation (Carnian) of NW Argentina. Ameghiniana. 44, 17R.
Ezcurra and Novas, 2008. A review of the dinosaur diversity of the Ischigualasto Formation (Carnian, NW Argentina): Insights on early dinosaur evolution. in Langer, Bittencourt and Castro (eds.). Boletim de Resumos, VI Simposio Brasileiro de Paleontologia de Vertebrados, Paleontologia, Edicao especial. Universidad de Sao Pablo: Ribeirao Preto. 88-89.
Ezcurra, 2010. A new early dinosaur (Saurischia: Sauropodomorpha) from the Late Triassic of Argentina: A reassessment of dinosaur origin and phylogeny. Journal of Systematic Palaeontology. 8(3), 371-425.
Ezcurra and Novas, in prep.

I can send a copy of any of the references if emailed at Mickey_Mortimer111@msn.com .

Holotype of Ankistrodon indicus (GSI coll.) in (A) lateral and (B) posterior views, with (C) a cross section of a tooth. After Huxley, 1865.

Comments- Huxley named and described the holotype, believing it to be a thecodont most similar to the parasuchian Clepsysaurus based on the presence of only distal serrations. He later (1870) referred Thecodontia to Dinosauria, leading him to refer Ankistrodon to the latter clade. Seeley (1880) mentioned the genus as a dinosaur related to Megalosaurus. He later (1885) created the genus Epicampodon for the taxon, since he incorrectly thought Ankistrodon was preoccupied by the recent viperid genus Agkistrodon Palisot de Beauvois, 1799 (or its own unjustified emmendation Ancistrodon Wagler, 1830; or the pycnodontiform fish Ancistrodon Roemer, 1849, which was renamed Ankistrodus then Grypodon). Seeley (1888) illustrated Epicampodon as an anchisaurid theropod, while Nopcsa (1901) listed it as an anchisaurine megalosaurid. It was listed as a zanclodontid theropod by Zittel (1890) and Huene (1902), who incorrectly believed it to be from the Late Triassic Maleri beds. Huene (1906) stated that the species was probably referrable to Thecodontosaurus, though he did not explicitly list the new combination until 1908. In that work he called it Thecodontosaurus(?) indicus, believing it to be most similar to Paleosaurus (his Thecodontosaurus cylindrodon). Das-Gupta (1931) thought the species was similar to his new theropod Orthogoniosaurus in having only distal serrations and having a straight distal edge (actually caused by apical breakage in indicus), placing both in Anchisauridae within Theropoda.

Huene still referred Epicampodon to Saurischia in 1940, but in 1942 recognized it was a more basal archosauriform and made it a species of Chasmatosaurus. This was followed by Tatarinov (1961), but Charig et al. (1976) correctly noted Ankistrodon has priority over Chasmatosaurus (and its senior synonym Proterosuchus). Charig and Reig (1970) and Reig (1970) considered it an indeterminate proterosuchian. Romer (1972) considered the material to be Proterosuchus without explicitly naming the new combination. Most recently, Charig et al. (1976) considered Ankistrodon a seemingly valid genus of proterosuchid, which was followed by Olshevsky (1991). While the presence of serrations does indicate an archosauriform, the Early Triassic age excludes parasuchians and theropods, and the recurved crowns exclude a relationship to sauropodomorphs like Thecodontosaurus or Anchisaurus, evidence supporting a close relationship with Proterosuchus was perhaps only given by Huene (1942), prior to the discovery of a large amount of 'proterosuchian' diversity. Recent analyses suggest that the traditional Proterosuchidae is a paraphyletic grade of basal archosauriforms, so Ankistrodon is here placed in Archosauriformes until further studies on mandibular and dental variation are performed.

Huxley (1865) also described vertebrae as belonging to Dicynodon orientalis (now Lystrosaurus murrayi), which were recognized by Huene (1942) as being archosauriform and referred to his Chasmatosaurus indicus. As the vertebrae cannot be compared to the type jaw fragment, Charig and Reig (1970) merely called them cf. Chasmatosaurus sp..

References- Huxley, 1865. On a collection of vertebrate fossils from the Panchet Rocks, Ranigunu, Bengal. Memoirs of the Geological Survey of India; Paleontologia Indica, Series IV. Indian Pretertiary Vertebrata. i, 3-24.

Huxley, 1870. Triassic Dinosauria. Nature. 1, 23-24.

Lydekker, 1880. A sketch of the history of the fossil Vertebrata of India. Journal and Proceedings of the Asiatic Society of Bengal. 69(2), 8-40.

Lydekker, 1885. The Reptilia and Amphibia of the Maleria and Denwa Groups. Memoirs of the Geological Survey of India. Palaeontologia Indica, Series IV. Indian Pretertiary Vertebrata. 1(5), 1-38.

Monday, November 15, 2010

It's been a while since my last post. Things have been busy around here with my new computer and the holiday season starting up, butb I'll try to post some entries I recently finished. Today we look at two of Paul's clades from DoA.

Comments- This clade was first suggested by Paul (1988) as a more appropriate name for Theropoda (as their feet are birdlike as opposed to beastlike), though he recognized Theropoda could not be renamed. In his later 2002 book, Paul actually proposed Avepoda as a subgroup of Theropoda, for those "that either possessed a foot in which metatarsal I did not contact the distal tarsals, or descended from such theropods, and belonged to a clade which includes Neotheropoda." The definition is here modified by using Allosaurus fragilis as the internal specifier, as that taxon is here used as the internal specifier of Theropoda. Avepoda has almost exclusively been used by Paul, with other authors using Neotheropoda (sensu Sereno) for the group since the two usually have the same known content (though Avepoda is near certainly more inclusive than Neotheropoda sensu Sereno, unless coelophysoids were the first theropods to develop the tridactyl pes). However, Procompsognathus was an avepod possibly outside the Coelophysis+Passer clade in Paul's (1988) phylogeny and Gauthier's (1986) analysis, as was Liliensternus in the latter. More recently, Liliensternus was found to be outside the Coelophysis+Passer clade in Bittencourt Rodrigues' unpublished thesis. Avepoda also has an advantage over Neotheropoda in only having one definition, whereas the latter can also apply to the more exclusive Ceratosaurus+Passer clade. Note it is not the same as Avipoda Novas, 1992, which was proposed for a clade similar in extent to Tetanurae.

Paleotheropoda was proposed as a paraphyletic order of theropods by Paul (1988), including all theropods which were not avetheropods. This consisted of what are generally recognized today as coelophysoids, ceratosaurs and megalosauroids, as well as a few other taxa such as Piatnitzkysaurus and sinraptorids. No other reference used the term due to the general dislike of paraphyletic groups, and in 2002 Paul referred to the same grade as baso-avepods. As Paul's (1988) Theropoda was equivalent to Avepoda, Paleotheropoda is catalogued here as a synonym of that group.

Comments- Paul (2002) proposed Averostra for a clade of "avepods that either possessed at least one accessory maxillary opening in the lateral wall of the antorbital fossa that led into a bony mediorostral maxillary sinus, or descended from such avepods, and are members of the clade that includes the Dromaeosauridae." This included taxa generally recognized as ceratosaurs and tetanurines, but excluded coelophysoids. The definition is here modified to use Dromaeosaurus albertensis (as the eponymous species for Dromaeosauridae) and to specify the promaxillary fenestra (as it is the first accessory maxillary opening to evolve, and the only one present in taxa Paul considers basal averostrans such as Ceratosaurus). Ezcurra has used Averostra for the ceratosaur+tetanurine clade in several papers, and in 2007 with Cuny gave it a new node-based phylogenetic definition with that extent- "Ceratosaurus nasicornis, Allosaurus fragilis, and all the descendants of their common ancestor." However, Paul's apomorphy-based definition may not be limited to that clade. Promaxillary fenestrae have since been identified in Dilophosaurus, Zupaysaurus, "Megapnosaurus" kayentakatae, herrerasaurids and Heterodontosaurus. Unfortunately, the phylogenetic position of most of these taxa is controversial, making it difficult to determine which clade an apomorphy-based Averostra designates. In a more traditional topology where coelophysoids are ceratosaurs and/or Dilophosaurus and/or Zupaysaurus are basal coelophysoids, Averostra encompasses at least Neotheropoda sensu Sereno. In alternative phylogenies where Zupaysaurus and/or Dilophosaurus are closer to birds than to Coelophysis, Averostra encompasses at least the former two taxa and perhaps Coelophysoidea (ambiguous since Megapnosaurus and Coelophysis lack promaxillary fenestrae). As derived ornithischians, sauropodomorphs, Eoraptor and Tawa all lack promaxillary fenestrae, it's not certain whether those of herrerasaurids and/or Heterodontosaurus are homologous to theropods'. In a phylogeny like Sereno's where herrerasaurids are sister to avepods (and presumably Tawa), Averostra may encompass the herrerasaurid+avepod clade. No standard topology (where sauropodomorphs and Eoraptor are closer to avepods than ornithischians are) results in Heterodontosaurus' promaxillary fenestra being homologous to theropods' though. With these caveats in mind, Averostra is here provisionally placed at the level of Avepoda.